Lassaigne trial
The Lassaigne probe , named after the French chemist Jean Louis Lassaigne (1800-1859), is a method for the detection of organic nitrogen or cyanide through the formation of easily soluble Prussian blue , which can be easily identified by its blue-green color.
The aqueous analysis - solution is diluted with sodium hydroxide solution or hydrochloric acid is neutralized . A little saturated iron (II) sulfate solution is then added dropwise and the mixture is briefly heated to the boil.
If cyanide is present, hexacyanoferrate (II) is formed :
- Fe 2+ + 6 CN - → [Fe (CN) 6 ] 4−
Then a little saturated iron (III) chloride solution is added dropwise and heated again.
If the hexacyanoferrate (II) had previously formed, the blue-green, easily soluble Berlin blue is now formed:
- [Fe (CN) 6 ] 4− + Fe 3+ → [Fe III Fe II (CN) 6 ] - (blue-green in solution)
- [Fe (CN) 6 ] 4− + Fe 3+ + Na + → Na [Fe III Fe II (CN) 6 ] (blue-green precipitate)
- [Fe (CN) 6 ] 4− + Fe 3+ + K + → K [Fe III Fe II (CN) 6 ] (blue-green precipitate)
Whether precipitation occurs depends on the number and type of alkali cations present .
See also
Individual evidence
- ^ Brockhaus ABC Chemie , VEB FA Brockhaus Verlag Leipzig 1965, p. 786.